Nobody can answer that question without a data sheet. If this is an instrument, then it may have a 50 ohm output impedance, so analyze as if there were a 50 ohm resistor in series. Or it may have settings for the output impedance, or a low impedance mode. I expect 50 ohms.

To test it, measure the open circuit pulse amplitude, then apply a 50 ohm load. The change in voltage will tell you the output impedance. It will go to 1/2 the voltage if it is a 50 ohm generator.